// 136.只出现一次的数字
var singleNumber = function (nums) {
  const map = new Map();
  for (const e of nums) {
    map.set(e, (map.get(e) || 0) + 1);
  }
  for (const element of map.entries()) {
    const [key, value] = element;
    if (value === 1) return key;
  }
};
